Remote imaging systems are used to view objects not normally accessible to human observation or conventional imaging tools. Only limited-size image transducers are positioned for viewing, and a signal is transmitted to a remote location for viewing. For instance, surgeons use optical probes to view internal anatomy for diagnosis or surgery. Such systems require miniaturized multi-wire cable assemblies to transmit images recorded by a charge coupled device (CCD) to an external display screen.
For surgical and other applications, it is desirable to minimize the cable size. Limited diameter facilitates desired flexibility. However, a detailed real-time image needs significant bandwidth, requiring many separate conductors of a given frequency capability. To avoid undesirably bulky cables when substantial numbers of conductors are required, very fine conductors are used. To limit electrical noise and interference at high signal frequencies, conductors are generally shielded. A typical approach employs fine coaxial wires, which are bundled in a cable. Each wire includes its own shield, which provides suitable protection against interference at high frequencies.
While adequate, multiple coaxial assemblies have several disadvantages. The manufacturing cost of fine coaxial wiring is higher than is acceptable for many applications. The mode of terminating very fine coaxial wire is complex and expensive. And coaxial wires generate unwanted bulk due to the need for a given spacing between core conductor and shield.
For low-voltage differential signal (LVDS) communication, twisted pair wiring has been used effectively. However, for the finest gauge wires and for high frequencies required in certain applications, twisted pair wires have critical limitations. One problem is that when twisted pairs are bundled together and surrounded by a suitable conductive shield layer, they have different electrical characteristics with respect to the shield. Some pairs will inevitably be closer to the shield than are others, resulting in common mode impedance differences or signal skew as signals via different pairs arrive at different times. Such skew limits usable signal rates, a particular concern with very small conductors needed for slim, flexible cables requiring a multitude of lines.
A further disadvantage of existing systems is that they lack a light source, requiring a second cable in the surgeon's hand to convey light via an optical fiber bundle. Coordination of separate cables makes surgery is difficult, and requires a larger surgical opening in the patient. Moreover, efforts to unify the two cables create a much stiffer cable lacking desired flexibility due to its overall size.